Incandescent electric lamp.



2 SHEETS-SHEET1- His fittorne g.

I. LANGMIEIR.

INCANDESCENT ELECHHC LAMP.

APPLICATION FILED APR. 19, m3.

I. LANGMUIR.

INCANDESCENT ELECTRIC LAMP.

APPLICATION FILED APR. 19. 1913.

1,180,159. Patented 1 ,1 8, 19111.

2 SHEETS-SHEET 2.

Fig.4.

xitfnessz 0n Inventor:

M Irving Langmuir, Q b W wwm H is Jlttorneg.

' of New York, have invented certain new .ness, as will be more fullyhereinafter set,

STATES PATENT OFFICE. I Item LANemnIn, or SCHENECTADY, irnw'vonnassmivon TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW INCANDESCEIVTELECTRIC LAMP.

Patented Apr. 18, 19] 6. Application filed April 1a, 1913. Serial No.762,327.

1,180,159. Specification of Letters Patent.

out danger of unduly softening the glass, and do not admit the drynitrogen until I have in this way removed from the glass as far aspossible all traces of water vapor.

The particular lamp shown is adapted to operate at a current of about 8amperes with an efliciency of about .7 to .8 watts per candle. At thisefiiciency the lamp has substantially the commercial useful life ofstandard lamps on the market at the present time, the drawn-wiretungsten lamps, which with a corresponding life have an efficiency ofabout 1 to 1% watts per. candle.

The efficiency of an incandescent lamp of a given type and constructionis in general directly related to its useful life, that is to say, alamp which 'will operate at 13; Watts per candle for 1,000 hours usefullife can be run at one watt per candle by simply increasing the Volta eto which it is sub- 10 jected, but the use ul life will bemuchshortened, and the same lamp set up at .5 watts per candle will beblackened and de- To all whom it may concern: I

Be it known that I, IRVING LANGMUIR, a'citizen of the United States,residing at Schenectady, county of Schenectady, State and usefulImprovements in Incandescent Electric Lamps, of which the following isa. specification. I y present invention relates to improve- 10 ments inincandescent electric lamps whereby it is *possible to produce a lampcapable of operating at extraordinarily high efficiency and giving alight of marked increase in intrinsic brightness and whiteforth. a

In the drawings attached to this specification, Figure 1 is a view of alamp embodying my invention, while Figs. 2, 3, 4 and 5 20 showmodifications within the scope of my invention. I

I will now proceed to describe in detail the lamp shown in Fig. 1, whichrepresents one particular type of lamp embodying my invention.

,1 is the lamp bulb, which is decidedly elongated; 2 is a filament oftungsten which may be constructed by any of the now wellowu squirting ordrawing processes. In thiscase the filament is about 10 mil s indiameter and about three-inches long. The filament is located near thebottom of the bulb .and is supported by heavy, stiff,- wrought tungstenwires 3, 4, connected through conductors 5 and 6 with theexternalterminals. .The lamp bulb is filled with nitrogen carefullypurified and free fromwater-vapor, admitted at a pressure which may beas low as say 50 mm. but which to advantage may be atmospheric when'thelamp, is cool. The bulb is finally sealed in the usual manner.

In the manufacture of the' lamp I dry' the gas by. carrying it a numberof times over phosphorous pentoxid, and further I thoroughly dry thebulb of the lamp and free it from adhering gases and water vapor byexhausting for a long time while it is heated in a suitable oven to atemperature as high as can practically be realized with- It was at onetime proposedto introduce nitrogen into the bulb of a lamp having acarbon filament, and, in order to reduce the convection losses, that"the filament should be reduced to a smaller cross section than usualheretofore? he lamp was a failure'for reasons which, in the light of the.work which I have done, can readily be pointed out. In the firstplace,as will appear more fully hereafter, thereduction of the cross-sectionof the filament was a step decidedly in 'the wrong direction, but alsovery serious is the chemical action between the nitrogen and the carbonof the filament, which at the temperature of incandescence react on eachother 'to form cyanogen, and

ultimately para-cyanogen. This action not only obscures the bulb by adeposit of a brown powder-ofjpara-cyanogen, but also destroys thefilament. It was also proposed to use cyanogen in place of nitrogen, butthis combination also is inoperative since the cyanogen decomposes anddeposits carbon on the filament, so that the size of the filamentcontinually increases and its resistance, continually decreases, and ifthe lamp be placed in multiple across the mains so that it'is suppliedwith constant potential, the action is a cumulative one, the lamp runsaway, that is to say, the filament grows in size and temperature untilin a few minutes it is destroyed, while if on the other hand it isoperated in series on a constant current circuit, its reduced resistancereduces its temperature and its efficiency is lost.

My experience has shown that it is necessary that certain relationsexist between the atmosphere of the lamp and the material of thefilament. The combination which I have found to be most suitable is theone above described. Tungsten possesses a great advantage over carbonwhich renders it highly suitable for use in my improved lamp, in that ithas not only a high melting point but also a very low vapor pressure athigh temperatures. The light emission from a lamp is inproportion to theeleventh power of the absolute temperature, so that a very slightincrease of temperature above that normally used in incandescent lampsbrings about a very considerable increase in efficiency. This increaseis sufficiently great in lamps constructed in accordance with myinvention to produce the striking results above described, in spite ofthe fact that a certain amount of heat is wasted by convection; butcarbon in an atmosphere of nitrogen or cyanogen, irrespective of thevital difficulties, above mentioned, has the property of slowlyvaporizing at temperatures corresponding-to three watts per candle, anda very sl ght increase of temperature causes a considerable increase inthe rate of vaporization; so that a carbon lamp operated either in avacuum or in the manner described by .Edison becomes blackened in a fewminutes if the efficiency be pushed even to two watts per candle.Moreover, with an efficiency of two watts per candle the life of acarbon filament up to the point of burn out is very short and whenoperated in nitrogen is very much shorter than when operated in avacuum.

One important feature of my invention consists in so correlating thefilament material with the atmosphere that-the atmosphere reduces thetendency of the material I to vaporize, and makes it possible to operatecommercially at higher efiiciencies i than can be realized with thesame-material in a vacuum.

filament, even at the high temperatures mentioned, though it may reacton tungsten vapor in the lamp, with the formation of nitrid of tungsten,a material which is less opaque than tungsten. In addition nitro gen ispeculiarly suitable as an atmosphere because of the fact that it has'alow heat conductivity.

The losses from the filament are of three sorts: first, the directradiation; second, the conduction through the atmosphere in the bulb;and third, convection. Direct radiation of energy from the filament isdesirable, since it is this radiation, or a portion of it, whichconstitutes the light. The other two losses are harmful and should beminimized as far as possible; in commercial practice they have beenreduced to the lowest limit by the use of a very high vacuum.

In place of nitrogen I may use various other gases or vapors, providedthat they are properly correlated to the material of the filaments. Forexample, I may use with a tungsten filament, which filament I haveheretofore found to be the best suited to my invention, an atmosphereconsisting of argon, or mercury vapor, or other gaseous filling havingsufficiently poor heat conductivity and satisfying the otherrequirements herein indicated. Carbon monoxid may also be used as anatmosphere in the lamp but is notas advantageous as those alreadymentioned. Hydrogen, however, is distinctly unsuitable because it hasgood heat conductivity and because it appears to dissociate at the hightemperatures at which the filament of my improved lamp must be run, thetemperatures being in excess of that of a tungsten filament whenoperating in a vacuum at an efficiency of one watt per candle. Thepressure of the atmosphere in the bulb should be relatively high. Iobtain good results for example with a pressure (measured when the lampis cold) of 300 millimeters of mercury, or as low as 50 millimeters, buthigher pressures are preferable, and indeed I usually employ pressuresof about one atmosphere. The pressure should not however be so high asto involve any danger of destroying the bulb when the filament isheated. Not only do these high pressures, when utilized in accordancewith my invention, reduce the tendency of the filament to vaporize orwaste away, but the convection currents set up in the gas surroundingthe filament serve to convey away from the vicinity of the filament anyvapor which may be emitted. By properly proportioning and designing theparts the material constituting this vapor may be deposited at portionsof the lamp where it is not objectionable. For example, in the lampshown in Fig. l the blacken the bulb and seriously reduce thetotahefiiciency, but in lamps constructed in accordance with thisfeature of my invention the life of the lamp is not so limited, and avery considerable loss of material from the filament can take place.From this point of view it is desirable to operate with filaments oflarge diameter. But there are other reasons why the diameter of thefilament has an important bearing on my invention. I have already spokenof the loss of energy by convection and'conduction; I have found thatwithin moderate limits these losses are approximately independent of thesize of the filament; that is to. say as be tween :1 filament 10 mils indiameter and a, filament 3 mils in diameter there is very .littledifference in the magnitude of the conduction and convection losses, butthe surface areas of the two filaments are in the '80 ratio of ten tothree, and as the light emission at'a given temperature is proportionalto the surface, the 10-mil filament will-radiate more than three timesas much light as the three-mil filament, and it is this fact, in

85 combination with the reduced vaporization obtained by suitable choiceof filament andatmosphere, and the other features of invention hereindescribed, which enables me to attain the efficiency above indicated.

40 In a lamp made in accordance with my invention, with a 10-milfilament operating at an efiiciency of .52 watts per candle, I find thatthe filament is operating at a temperature which, if the filament werein'vacuum,

'46 would correspond to an efiiciency of 0.37 watts'per candle; thedifference of 0.15 watts represents the convection and conductionlosses. Of course if an attempt be made to operate an ordinary tungstenfilament incandescent lamp at any such efiiciency as 0.37

or even 0.52 it rapidly blackens and is destroyed. By employingfilaments of still larger diameter, and especially if they beconcentrated by coiling-or otherwise, the efii' ciency may be stillfurther raised. Thus I have caused lamps to be constructed in accordancewith my invention having coiled or helically-wound filaments of tungstenwire of 20 mils in diameter and operating 760 with a current in theneighborhood of 20 amperes. The candle power was comparable to that ofan arc lamp and the efficiency was about 1 of a watt per candle. Owingto the large size of this lighting unit the bulb was '65 made very largeto avoid overheating.

An incidental but valuable result of my. invention is the elimination ofthese-called Edison effect, which renders-thelamps of my inventionpeculiarly suitedffbrhigh-volt- 4 age work, though the large filamentswhich I find give the best results also render the lamps suitable forseries circuits carrying currents of considerable magnitude, on whichthe voltage consumed in eachlamp is usually relatively low.

The advantages of a large filament may to a considerable extent berealized by the use of a small filament in concentrated form as a coilor spiral form, as shown in Fig. 2. Moreover, as already-indicated, thewinding of a large diameter filament in concentrated form, as'bycoiling, still further increases the efficiency attainable. Fig. 3 showsa lamp in which the spiral filament 12 is located practically at thecenter. of the bulb 13 and is supported by heavy bare tungsten leads 14.The lamp .of Fig. 3

. diflers from the lamp of Fig. 2 inthat the bulb is spherical insteadof elongated. In thiscase the bulb must be of considerable 9 size, andin fact in all cases it is better that the bulb should be of relativelylarge size with respect to the filament in order to avoid overheating.

The heavy tungsten leads 14 are capable i of enduring the intense heatof the gases without giving ofl water-vapor, and these gases as theyrise become cooler so that when: they reach the seal 15 and theadjacentglass parts, they are prepared to deposit the tung- 1 sten whichthey carry with them and at the same time do not 'cause harmful heating.I find however that the use of long tungsten leads, though highlydesirable, is not essential. For example, in Fig. 4 and Fig. 5 I haveshown an arrangement by which the filament may be so supported that thehot gases which arise from it do not come in contact with the seal orwith the supports. This result is secured in Fig. 4 by locating thefilament 16 above the seal or glass support 17, in which case thefilament may be carried by short leads 18, which may be of tungsten,molybdenum, or other suitable material, which may extend up from theseal '17. Similarly in Fig. 5, the seal 19 extends in from the side ofthe bulb horizontally.

What I claim as new and desire to-secure by Letters Patent of the UnitedStates, is,

1. In an incandescent lamp, the combination of the closed lamp bulb, agaseous filling therein of substantial pressure at the operatingtemperature of the lamp and of substantially poorer heat conductivitytham hydrogen, and a filament of such high melting point and low vaporpressure that it may be operated during a long useful life at atemperature higher than that of a tungsten filament operating in avacuum at an efliciency of one watt per candle. 139

2. In an incandescent lamp, the cbmbinatlon of the lamp bulb, a gaseousfilling therein of considerable pressure at the operating temperature ofthe lamp and of poor heat conductivity, and a filament of metal havingsuch high melting point and low vapor pressure that the filament may beoperated during a commercially useful life at a temperature higher thanthe temperature of the filament of a vacuum tungsten lamp operating atan efficiency of one watt per candle.

3. In an incandescent lamp, the combination of the lamp bulb, a gaseousfilling therein of substantial pressure at the operating temperature ofthe lamp and having a heat conductivity poorer than that of hydrogen,and a filament of large effective diameter and of metal having highmelting point and low vapor pressure so that the filament may beoperated during a long useful life at a temperature and at an efiiciencyhigher than would be permissible to give the same useful life if thefilament were operated in a vacuum.

4.- The combination of a lamp bulb, a filling therein of dry nitrogen ata pressure materially in excess of that corresponding to 50.-millimetersof mercury and a filament of tungsten of large effective diameter, thefilament being thereby adapted for operation at a temperature higherthan that which it would have if operated in a vacuum at an efficiencyof one watt per candle.

5. An incandescent electric lamp having a filament of tungsten of largeeffective diameter anda bulb or globe therefor filled with dry nitrogenat a pressure as high or higher than that corresponding to 300millimeters of mercury, the filament being thereby adapted for operationat a temperature higher than that which it would have ifoperated in avacuum at an effieiency of one watt per candle.

6. An incandescent electric lamp having a filament of large effectivediameter formed of refractory metal having very low vapor pressure, anda bulb therefor filled with a gas of poorer heat conductivity thanhydrogen and at a pressure exceeding that corresponding to 50millimeters of mercury, the filament being thereby adapted for operationat a temperature higher than that which it would have if operated in avacuum at an efliciency of one watt per candle.

7. An incandescent lamp consisting of a lamp bulb, a filament of amaterial having a high melting point and low vapor pressure locatedtherein, the upper portion of the lamp bulb serving as a condensingchamber or deposit chamber for material vaporized from the filament, agas or. vapor of poorer heat conductivity than hydrogen and of apressure materially in excess of that corresponding to 50 millimeters ofmercury, and a filament so proportioned in size that the lamp will emitlight at an efficiency higher than the efficiency the filament wouldhave in a vacuum if operated pof as to have approximately the sameuseful 8. An incandescent lamp having a lamp bulb provided with a. spaceserving as a depositchamber, a filament of a material having a highmelting point and low vapor pressure located below the deposit chamber,and an atmosphere in the bulb consisting of a pressure of gas or vapormaterially in excess of 50 millimeters of mercury and having poorer heatconductivity than hydrogen. 1

9. An incand'escent lamp having a lamp bulb provided with a spaceserving as a deposit chamber, a filament located below the depositchamber, and an atmosphere in the bulb consisting of a pressure of apoor heat phere in the bulb of relatively high pressure and of poorerheat conductivity than hydrogen, of a filament of a material having ahigh melting point and low vapor pressure and capable of operationwithout undue blackening of the bulb for a reasonable commercial life atan efliciency higher than could be obtained with the same length of lifewith such a filament in a vacuum.

11. The combination of a closed bulb or container, a gaseous fillingtherein of a pressure when the device is in operation materially inexcess of that corresponding to 50 millimeters of mercury and ofsubstantially poorer heat conductivity than hydrogen, and a filament oflarge effective diameter, and of material of such high melting point andlow vapor pressure that it may be operated during a long useful life atan efficiency better than one watt per candle.

12. In an incandescent lamp, the combination of the lamp bulb, atungsten filament therein, and a gaseous filling, the effective diameterof the filament being sufiiciently large and the heat conductivity ofthe filling being sufficiently poor to permit the lamp to be operatedwith a filament temperature in excess of that of a vacuum tungsten lampoperating at an efficiency of one watt per giving the efi'ect of afilament of large diameter, an inclosing bulb and a filling of gashaving a materially poorer heat c0117.

ductivity '5 as high 0 mercury, the filament being eration in turehigher than'that which it would have,

than hydrogen and at a pressure r higher than 300 millimeters of adaptedfor opsaid gaseous filhng at a tempera M if operated in a vacuum at anefiiciency of W. J. GREGAN, LEO C. Foss.

